纳米超微晶Fe73.5Cu1Mo3Si13.5B9合金显微结构和磁性的研究

对纳米晶Fe_73.5Cu₁Mo₃Si_13.5B₉合金的原始制备态和各退火态样品进行了室温Mossbauer谱研究,结果表明晶化态的合金存在α-Fe(Si)微晶相和晶界的非晶相。晶相和非晶相内场和面积随退火温度的变化是退火时Cu,Mo,B等成分的扩散和在各相中的再分配引起的。最佳磁性能对应非晶相中的铁量占合金铁总量的30％左右,超微晶合金的双相无规各向异性模型表明,一定量的非晶相对保持纳米晶优异的软 关键词：     

铁基纳米晶合金介观结构的等效RLC并联模型

根据实验研究成果提出纳米晶合金软磁性能受其介观结构影响的观点，建立了Fe基纳米晶合金的球状介观结构模型，分别求出只有交变磁场或交变磁场和静磁场作用时纳米晶粒球的频率函数——D函数.分析表明，两种D函数都是复变函数，其实部Re(D)为纳米晶电感性质和电容性质的反映，虚部Im(D)为纳米晶电阻性质的反映，据此建立了Fe基纳米晶合金介观结构的等效RLC并联模型.由该模型求得合金产生极值巨磁电阻的条件为v_extGMI=v|_Re(D)=0，决定因素有μ,σ,ω,R和H_ex及微观磁结构. 关键词： Fe基纳米晶合金 等效RLC并联模型 球状介观结构模型 频率函数     

Fe39.4－xCo40Si9B9Nb2.6Cux纳米晶合金的有效磁各向异性研究

采用多晶材料趋近饱和定律研究了非晶Fe_39.4-xCo₄₀Si₉B₉Nb_2.6Cu_x(x=0.5,1,1.5) 合金在不同温度纳米晶化后的有效磁各向异性常数〈K〉.结果表明， Cu含量较低(x=0.5)时，纳米晶粒较大并且在较低的退火温度(550℃)下析出硬磁相，〈K〉随退火温度T_a升高显著增加；随着Cu含量的增加，有效地细化了晶粒，并且抑制了硼化物的析出，〈K〉明显减小.讨论了〈K〉与晶粒尺寸D及初始磁导率的关系. 关键词： 纳米晶 有效磁各向异性 磁导率 FeCo基合金     

CoFe2O4纳米颗粒的结构、磁性以及离子迁移

聚乙烯醇(PVA)溶胶凝胶法制备出CoFe₂O₄纳米微粉，用X射线衍射研究了铁氧体纳米颗粒的结构.测量了CoFe₂O₄纳米颗粒80—873 K的变温穆斯堡尔谱，发现纳米颗粒的磁转变温度范围为793—813 K，比块体材料的磁性转变温度要低.CoFe₂O₄纳米颗粒的德拜温度θ_A=674 K，θ_B=243 K，比块体材料要小.CoFe₂O₄纳米颗粒超精细场H_f随温度的变化符合T^3/2+T^5/2定理.当温度较高时，平均同质异能移IS随温度的升高而减小，并呈线性关系. 关键词： 纳米颗粒 磁性 穆斯堡尔谱     

Al-Ni-RE非晶合金的晶化行为和热稳定性

本文制备了一系列Al-Ni-RE (RE=La, Ce, Y) 非晶合金薄带, 利用差示量热扫描仪和X射线衍射仪考察了非晶合金的晶化行为和初生相, 并分析了其与合金成分和原子特性间的关系. 结果表明: 在拓扑不稳定参数λ以有效原子半径修正为λ'后, 每一Al-Ni-RE非晶合金体系可由其两个临界值划分为纳米晶、纳米玻璃和玻璃三类; Al-Ni-RE非晶合金的晶化开始温度和混合焓与λ'成良好的线性关系, 即λ'能很好的表征Al基非晶合金的热稳定性. 关键词： Al基非晶 玻璃转变 初生相 热稳定性     

退火加热速度对Fe-Cu-Nb(V)-Si-B纳米晶合金磁性的影响

研究了退火温度为550℃的纳米晶化过程中加热速度对Fe_72.7Cu₁Nb₂V_1.8Si_13.5B₉与Fe_73.5Cu₁Nb₃Si_13.5B₉合金磁性的影响．磁性测量结果表明，退火加热速度对这两种合金软磁性能有明显的影响，快速加热可显著提高合金的初始磁导率μ_{i 关键词：}     

块体非晶合金的黏度与玻璃形成能力的关系

基于经典结晶理论讨论了非晶合金的晶化动力学因素和晶化热力学因素对玻璃形成能力（GFA）的影响.分析表明,合金的等温转变（TTT）曲线“鼻尖”温度T_n对应的黏度与晶化阻力因子成正比;重新加热时晶化开始温度T_x对应的黏度与晶化驱动力因子成反比.由此得到了新的GFA参数ω₀=（T_g-T₀）/（T_x-T₀）-（T_g-T₀）/（T_n-T₀）,其中T_g为玻璃转变温度,T₀为理想玻璃转变温度.统计结果显示,ω₀与临界冷却速率具有较高的相关性,R²高达09626.进一步分析表明：新提出的ω₀参数可以合理地解释过冷熔体的黏度、脆性、液相稳定性、热稳定性以及T_rg、ΔT_x、γ、γ_m、ΔT_rg、α、β、δ和φ等参数与GFA的关系. 关键词： 块体非晶合金 黏度 脆性 玻璃形成能力     

基于Al2O3/Pt纳米晶/HfO2叠层的MOS电容存储效应研究

采用电子束蒸发Pt和后快速热退火的方法,研究了退火条件对Pt纳米晶的生长特性的影响,结果显示Pt纳米晶的密度随退火温度的升高和退火时间的延长均表现出先增大后减小的趋势.在800℃下退火20 s能得到分布均匀的、密度为30×10¹¹ cm^-2的Pt纳米晶.进一步研究了基于Al₂O₃/Pt纳米晶/HfO₂叠层的MOS电容结构的存储效应,表明其在-3—+8 V扫描电压范围下C-V< 关键词： Pt纳米晶 快速热退火 原子层淀积 存储效应     

Zr60Al15Ni25大块非晶合金晶化动力学研究

通过等温示差扫描量热法研究了Zr₆₀Al₁₅Ni₂₅大块非 晶合金的晶化动力学.实验结果表明，晶化过程的孕育期很短，即使在743 K这样低的温度下也不过0.52 min，而放热峰宽（反应整个晶化过程进行的时间）却随退火温度的降低明显增大，这说明了结晶过程是一个晶核长大控制的过程.Avrami指数表明在不同的退火温度，该合金的晶化机制发生了变化.晶化机制的变化是由于合金原子在不同温度下的扩散能力相差很大所致. 关键词： 晶化动力学 60Al₁₅Ni₂₅大块非晶合金')" href="#">Zr₆₀Al₁₅Ni₂₅大块非晶合金 示差扫 描量热法（DSC）     

Pr2Fe14(C,B)/α-(Fe,Co)型纳米晶复合磁体的结构与磁性

研究了Pr_xFe_82-x-yTi_yCo₁₀B₄C₄ (x=9—10.5;y=0, 2)纳米晶薄带的结构与磁性. 结果表明,所有薄带皆主要由2∶14∶1, 2∶17和α-(Fe, Co)三相组成. 对于y=0的合金,其内禀矫顽力随Pr含量x的增加而增加,剩磁随Pr含量x的增加而减小. 以Ti置换部分Fe (y=2),合金的磁性能得到显著提高,表现为:添加Ti后,合金的剩磁B_r基本不降低,x=10.5时合金的B_r值甚至有较明显的提高;同时添加Ti后,合金的内禀矫顽力及退磁曲线的方形度都明显改善. 当x=10.5,y=2时,合金薄带的磁性能达到最佳值为: B_r=9.6 kGs(1 Gs=10^-4 T),_iH_c =10.2 kOe(1 Oe=79.5775 A/m)和(BH)_max＝17.4 MGOe. 随着Pr含量的提高,合金中的硬磁相2 ∶14 ∶1的含量相对增加,内禀矫顽力提高;而Ti置换Fe抑制了软磁相α-(Fe, Co)在快淬和热处理过程中的优先长大,使合金中软磁相和硬磁相的晶粒尺寸及比例趋向最佳组合,交换耦合作用明显增强. 关键词： 纳米晶永磁材料 2Fe₁₄(C')" href="#">Pr₂Fe₁₄(C B) Ti添加 交换耦合     

Magnetization behavior and magnetocaloric effect in bulk amorphous Fe60Co5Zr8Mo5W2B20 alloy

Microstructure by X-ray diffraction and Mössbauer spectroscopy, and isothermal magnetic entropy changes in the bulk amorphous Fe₆₀Co₅Zr₈Mo₅W₂B₂₀ alloy in the as-quenched state and after annealing at 720 K for 15 min are studied. The as-cast and heat treated alloy is paramagnetic at room temperature. The quadrupole splitting distribution is unimodal after annealing indicating the more homogenous structure in comparison with that for the as-cast alloy. Curie temperature slightly increases after annealing from 265±2 K in the as-quenched state to 272±2 K and the alloy exhibits the second order magnetic phase transition. The maximum of isothermal magnetic entropy changes appears at the Curie points and is equal to 0.30 and 0.42 J/(kg·K) for the alloy in the as-quenched state and after annealing, respectively. In the paramagnetic region the material behaves as a Curie-Weiss paramagnet.     

Annealing effect on soft magnetic properties and magnetoimpedance of Finemet Fe73.5Si13.5B9Nb3Au1 alloy

Effect of annealing on the soft magnetic properties of Fe_73.5Si_13.5B₉Nb₃Au₁ amorphous ribbon has been investigated by means of structure examination, magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) spectra measured in the frequency range of 1–10 MHz at a fixed current of 10 mA X-ray diffraction analysis showed that the as-cast sample was amorphous and it became nanocrystalline under a proper heat treatment. When annealing amorphous alloy at 530 °C for 30, 60, 90 min, soft magnetic properties have been improved drastically. Among the samples investigated, the sample annealed at 530 °C for 90 min showed the softest magnetic behavior. The MIR and PR curves revealed the desirable changes in anisotropy field depending upon annealing.     

Microstructure and some magnetic properties of bulk amorphous (Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)100−xYx (x=0, 2, 3 or 4) alloys

Microstructure, revealed by X-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy, and magnetic properties such as magnetic susceptibility, its disaccommodation, core losses and approach to magnetic saturation in bulk amorphous (Fe_0.61Co_0.10Zr_0.025Hf_0.025Ti_0.02W_0.02B_0.20)_100−xY_x (x=0, 2, 3 or 4) alloys in the as-cast state and after the annealing in vacuum at 720 K for 15 min. are studied. The investigated alloys are ferromagnetic at room temperature. The average hyperfine field induction decreases with Y concentration. Due to annealing out of free volumes its value increases after the heat treatment of the samples. The magnetic susceptibility and core losses point out that the best thermal stability by the amorphous (Fe_0.61Co_0.10Zr_0.025Hf_0.025Ti_0.02W_0.02B_0.20)₉₇Y₃ alloy is exhibited. Moreover, from Mössbauer spectroscopy investigations it is shown that the mentioned above alloy is the most homogeneous. The atom packing density increases with Y concentration, which is proved by the magnetic susceptibility disaccommodation and approach to magnetic saturation studies.     

Recoilless fraction, structural, magnetic and thermal properties of Fe73.5Cu1Nb3Si13.5B9 alloy

Differential scanning calorimetry, X-ray diffraction and room temperature Mössbauer spectrum measurements of Fe_73.5Cu₁Nb₃Si_13.5B₉ (Finemet) alloy have been carried out in order to study its structural and magnetic properties as a function of annealing temperature. The DSC profile of as-quenched Finemet showed two exothermic peaks at 530 and 702 °C, corresponding to two crystallization processes. The Finemet alloy remains amorphous at 450 °C with one broad peak in XRD pattern and one broad sextet in Mössbauer spectrum. When the Finemet alloy was annealed at 550 °C, only well indexed body-center-cubic phase was detected. After being annealed at 650 and 750 °C, the XRD patterns showed the coexistence of α-Fe(Si) and Fe-B intermetallic phases with the increase in XRD peak intensities, indicating the growth of crystallites and the decomposition of Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy at elevated temperatures. The Mössbauer spectra of annealed Finemet alloy could be fitted with 4 or 5 sextets and one doublet at higher annealing temperatures, revealing the appearance of different crystalline phases corresponding to the different Fe sites above the crystallization temperature. The appearance of the nanocrystalline phases at different annealing temperatures was further confirmed by the recoilless fraction measurements.     

Structural transformations and magnetic properties of Fe60Pt15B25 and Fe60Pt25B15 nanocomposite alloys

Structural and magnetic properties of two rapidly solidified and post-annealed Fe₆₀Pt₁₅B₂₅ and Fe₆₀Pt₂₅B₁₅ alloys are compared. The as-quenched Fe₆₀Pt₁₅B₂₅ ribbon was fully amorphous whereas in the Fe₆₀Pt₂₅B₁₅ alloy the amorphous phase coexists with an fcc FePt disordered solid solution. Differential scanning calorimetry curves of both alloys reveal a single exothermal peak with onset temperatures of 873 and 847 K for Fe₆₀Pt₁₅B₂₅ and Fe₆₀Pt₂₅B₁₅, respectively. Magnetically hard, tetragonal ordered L1₀ FePt and magnetically soft Fe₂B nanocrystalline phases were formed due to the annealing of the alloys, as indicated by X-ray diffraction and Mössbauer spectroscopy measurements. Two-phase behavior was detected in the temperature dependence of magnetization of the annealed samples. A magnetic hardening was observed for all annealed ribbons. Magnetic properties of the annealed alloys, studied by hysteresis loop measurements, were related to the differences in the relative fractions of the hard and soft magnetic phases calculated from Mössbauer spectra. The alloy with 25 at% Pt exhibits better hard magnetic properties (H_c=437 kA/m, M_r/M_s=0.74) than the alloy with smaller Pt content (H_c=270 kA/m, M_r/M_s=0.73) mainly due to the larger abundance of the ordered tetragonal FePt phase.     

The effect of different temperature annealing on phase relation of LaFe11.5Si1.5 and the magnetocaloric effects of La0.8Ce0.2Fe11.5−xCoxSi1.5 alloys

The phase relation of LaFe_11.5Si_1.5 alloys annealed at different high-temperature from 1223 K (5 h) to 1673 K (0.5 h) has been studied. The powder X-ray diffraction (XRD) patterns show that large amount of 1:13 phase begins to form in the matrix alloy consisting of α-Fe and LaFeSi phases when the annealing temperature is 1423 K. In the temperature range from 1423  to 1523 K, α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase, and LaFeSi phase is rarely observed in the XRD pattern of LaFe_11.5Si_1.5 alloy annealed at 1523 K. With annealing temperature increasing from 1573  to 1673 K, the LaFeSi phase is detected again in the LaFe_11.5Si_1.5 alloy, and there is La₅Si₃ phase when the annealing temperature reaches 1673 K. There almost is no change in the XRD patterns of LaFe_11.5Si_1.5 alloys annealed at 1523 K for 3-5 h. According to this result, the La_0.8Ce_0.2Fe_11.5−xCo_xSi_1.5 (0≤×≤0.7) alloys are annealed at 1523 K (3 h). The analysis of XRD patterns shows that La_0.8Ce_0.2Fe_11.5xCo_xSi_1.5 alloys consist of the NaZn₁₃-type main phase and α-Fe impurity phase. With the increase of Co content from x=0 to 0.7, the Curie temperature T_C increases from 180 to 266 K. Because the increase of Co content can weaken the itinerant electron metamagnetic transition, the order of the magnetic transition at T_C changes from first to second-order between x=0.3 and 0.5. Although the magnetic entropy change decreases from 34.9 to 6.8 J/kg K with increasing Co concentration at a low magnetic field of 0-2 T, the thermal and magnetic hysteresis loss reduces remarkably, which is very important for the magnetic refrigerant near room temperature.     

Synthesis, characterization and magnetic properties on nanocrystalline BaFe12O19 ferrite

Single phase BaM (BaFe₁₂O₁₉) ferrites are prepared by using sol–gel method. The preparing conditions of samples are investigated in detail, such as acid/nitrate ratio, the value of pH and annealing temperature. The best conditions on preparing BaFe₁₂O₁₉, which can be obtained on a Fe/Ba ratio of 12, the citric acid contents R = 3, the starting pH of solution is 9, and annealing temperature 950 °C. The thermal decomposition behavior of the dried gel was examined by TG–DSC, the structure and properties of powders were measured respectively by XRD techniques. The magnetic properties of barium ferrites are emphatically researched about the changing crystallite size and annealing temperature by the vibrating sample magnetometer (VSM). Magnetic measurement shows that the barium ferrite samples annealed at 1000 °C has the maximal coercive field of 5691.91 Oe corresponding to the maximal remnant magnetization of 35.60 emu/g and the sample synthesized at 1000 °C has the maximal saturation magnetization of 60.75 emu/g.     

Magnetic properties of a Pt/Co2FeAl/MgO structure with perpendicular magnetic anisotropy

Microstructures and magnetic properties of Ta/Pt/Co 2 FeAl（CFA）/MgO multilayers are studied to understand perpendicular magnetic anisotropy（PMA） of half-metallic full-Heusler alloy films.PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope.It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA.The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature.At the intersection points,the decreasing slope of the saturation magnetization（M s） changes because of the conversions.The dependence of M s on the annealing temperature and MgO thickness is also studied.     

Detection of structural and magnetic transitions in La0.67Ba0.23Ca0.1MnO3 using the rf resonance technique

We report radio-frequency (rf) electrodynamics in polycrystalline La_0.67Ba_0.23Ca_0.1MnO₃ as a function of temperature and magnetic field using a home-built LC resonant circuit powered by an integrated chip oscillator. The resonance frequency (f_r) of the oscillator and the power (P) absorbed by the sample are measured simultaneously. The paramagnetic to ferromagnetic phase transition in the absence of an external magnetic field is accompanied by a rapid decrease in both P and f_r around the Curie temperature T_C=300 K. However, much below T_C, the f_r shows a step-like anomaly around 165 K (195 K) while cooling (warming), which we attribute to a structural phase transition from high temperature rhombohedral () to low temperature orthorhombic (Imma) phase. The step-like anomaly in f_r versus T disappears in a field of 300 G. Fractional changes as large as 19% in Δf_r/f_r and 10% in ΔP/P are observed under H=1 kG around T_C. Our study suggests that the rf resonance technique is a versatile tool to study the magnetization dynamics as well as to investigate the structural phase transition in manganites.     

Field-induced structural transition and the related magnetic entropy change in Ni43Mn43Co3Sn11 alloy

Magnetic properties and magnetic entropy change ΔS were investigated in Heusler alloy Ni₄₃Mn₄₃Co₃Sn₁₁. With decreasing temperature this alloy undergoes a martensitic structural transition at T_M=188 K. The incorporation of Co atoms enhances ferromagnetic exchange for parent phases. Austenitic phase with cubic structure shows strong ferromagnetic behaviors with Curie temperature T_C^A at 346 K, while martensitic phase shows weak ferromagnetic properties. An external magnetic field can shift T_M to a lower temperature at a rate of 4.4 K/T, and a field-induced structural transition from martensitic to austenitic state takes place at temperatures near but below T_M. As a result, a great magnetic entropy change with positive sign appears. The size of ΔS reaches 33 J/kg K under 5 T magnetic field. More important is that the ΔS displays a table-like peak under 5 T, which is favorable for Ericsson-type refrigerators.